Frequency changing device



1935- R. v. 1.; HARTLEY 2,010,665

' FREQUENCY CHANGING DEVICE Filed Jan. 15, 1935 INVENTOR R. V.L./-/AR7'LEY ATTORNEY.

Patented Aug. 6, 1935 I UNITED STATES PATENT caries 2,010,565 rnsoUENcY CHANGING nrzvroE Ralph V. L. Hartley, South Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 15, 1935, Serial No. 1,87ll

Claims. (Cl. 172-281) This invention relates to frequency converters quency pq, permitting a large current comand more particularly to arrangements for prop n nt f fr q n y H to fl w i to the ducing currents of reduced frequency with reput transformer T2 and substantially suppressing spect to that of the energy source. all other frequency components in the output 5 In accordance with the invention, frequency transformer T2. In the tuning of these circuits 5 conversion is effected through the agency of a the leakage inductance of the transformers reactance device included in an electric circuit, should be taken into account. This may be done the reactance of the said device being variable by modifying the values Of'Ll and L2. The imwith the current or voltage in the circuit by pedance Zp-q represents the impedance of the virtue of a mechanical motion of its parts. In system to which power at frequency pq is de- 10 the systems of the invention the variable -relivered. Lis an iron core coil placed between the actance may comprise an ironcored inductance arms of. a tuning fork F and of such a length coil, the inductance of which is varied by the that, except for thin air-gaps, the magnetic path motion of an armature mounted on a tuned reed consists of the iron core and the tuning fork F.

or tuning fork or may consist of an air condenser, The tuning fork F has a natural resonant fre- 1 one plate of which is capable of vibration at a quency of q cycles per second. fixed frequency. When the generator Ep is connected into the- By the proper tuning of the electrical circuit system by closing switch $1, a transient response and the mechanical vibrators, it has been found is excited (as in all dynamic systems) having possible to produce currents of a frequency lower frequency components at the impressed fre- 20 than that of the impressed exciting current and quency and at the resonant frequencies of the related thereto by the frequency of the mesystem. There will be a current component of chanical vibrator. In one arrangement of the frequency 1) in the C1, L1, T1 mesh, a current invention the current of reduced frequency has a component of frequency p-q in the C2, L2, T2

frequency equal to the difference between the mesh, and a, mechanical vibration, of frequency 25 frequency of the exciting current and the resq, of the tuning fork F. chance frequency of the mechanical vibrator. In a linear system the transient components at In a modified form currents of two frequencies other than the impressed frequency would have are produced, the sum of which is equal to twice no energy source to sustain them, consequently the impressed frequency. they would quickly be damped out, the system 30 The nature of the invention and its mode of settling down to sinusoidal oscillations at the operation will be more fully understood from the impressed frequency (1)). Here the magnetic following detailed description and by reference coupling of the electric and the mechanical sys- 0 e tac drawing of which: tem is non-linear, due to the fact that the me- Fig. 1 shows in schematic arrangement one chanical force on the fork F, produced by the 5 embod t of t e inVentiOn; flux across the air-gap, is proportional to the Figs. 2 and 3 inclusive, illustrate alternative square of the flux. This non-linearity affects thearrangements of the invention operating on the electrical system through the changing of the Sa e Principle as that Of and width of the air-gap as the fork vibrates, thereby Figs. 4 and 5 show alternative arrangements changing the inductance. 40 of a modified form of the invention. Modulation takes place as the result of this Referring to Fig. 1, Ep is a source of sinusoidal non-linearity. The current components of freelectromotive force of frequency p cycles per quency p nd p -q interact to produce their dif- Sefiond which is connected to the y em t ugh ference frequency q. This frequency component a switch S1. T1 is an input s er th ough in the flux produces a corresponding mechanical 45 which the electroinotive force is impressed on force across the air-gaps which reenforces the the electromechanical system. C1 and L1 are a mechanical vibrations. Simultaneously the mecondenser and inductance respectively, which are chanical motion produces a component of freof such magnitude. that, through resonance with quency q in thefiux due to the variation in the so the effective inductance of the system, they permagnetic path. This component modulates with mit a large current of frequency 32 to flow, but the flux component of frequency 11 to produce the substantially suppress any flow of current comdifference frequency p-q, thus reenforcing the ponents of other frequencies. Ca and L2 are recurrent component of frequency p-q. 3ecause of spectively a condenser and an inductance adthis process of mutual reenforcement with energy justed to resonate the output system to a fredrawn from the generator and transferred by modulation, the transient disturbances of frequency q and H do not die out but will, if the losses are sufliciently small and the impressed force sufiiciently large, built up and stabilize to steady oscillations.

The arrangement thus operates as a frequency changer delivering to the load a current of a frequency equal to the difference between that of the source and the resonance frequency of the vibrating element. These frequencies may be so related that the output is at a sub-harmonic of the supply frequency, but this relationship is not necessary. The tuning of the electrical circuits should be such as to produce electrical resonances at the frequencies indicated, but exact tuning is not necessary. It is necessary only that the impedances be low to currents of the respective frequencies.

Fig. 2 shows a modification in which the electromechanical coupling is electrostatic instead of magnetic. C represent plates of parallel plate condensers. The other plate of each of these condensers is an arm of the tuning fork F. The circuit resonances are obtained by means of a suitable choice of inductances and capacities L1, L2, C1 and C2 as before. The non-linearity is of essentially the same type as in the system of Fig. 1 since the mechanical force on the fork is proportional to the square of the charge on the condenser and the capacity reactance is varied by the variation in the spacing between the condenser plates when the fork vibrates.

A balanced form of the electrostatically coupled system is shown in Fig. 3. The input transformer T1 has a mid-tap in the secondary winding. This mid-tap is connected through the primary winding of an output transformer T2 to ground G. The tuning fork F has plates C mounted on both 'sidesof each arm and is itself grounded at G.

The condensers C between the arms of the fork are connected through-an inductance L1 to one side of the input transformer. The'condensers C, on the outside of the arms of the tuning fork,- are connected through'an'inductance L1 to the other side of the input transformer. The modulation by which the oscillations at frequencies p--q and q are sustained takes place as in the circuit of Fig. 2. The advantage of this form of the circuit is in a more complete separation of the electrical components. It is evident from the symmetry that no component of current of frequency 11 will be present in the mid-branch; thus the impressed frequency component is balanced out of the output much more readily than it can be suppressed by means of tuned circuits as in the previously described systems. When the arms of a forkvibrate they always move'in opposite directions. Thus, when the motion of the arms of the fork F increases the capacity of the outside condensers C it decreases the capacity of the inside condensers 'C,-, making the modulation products fiow in the mid-branch, through the output transformer T2. From the symmetry it is evident that-the current component of frequency H will divide and flow in equal magnitudes both directions from the mid- ,tap in the secondary of the input transformer thus balancing out the primary of the input systern. By a suitable choice of the inductances L1 and the-input and output transformersTi and T2 the system may be resonated to both the frequencyfcomponents p and pq.

In 4 isshown a different form of an electrostatically coupled device; The input network, consisting of a source of sinusoidal electromotive force of frequency 9, E an input transformer T1,

and a tuning inductance L1 and capacity C1, is as before. The condenser plates C are mounted to form condensers with the arms of a tuning fork F. In series with the primary of the output transformer T2 is a condenser C2 and inductance L2. The power delivered to the terminating network (represented by Zq) is at a frequency q. shunted across the output transformer T2 and the condenser C2, is-an inductance L3 in series with a condenser C3."

The resonant frequency of the tuning fork is, in this case, in. By means of a suitable choice of La and C: the system is given an electrical reso nance at a frequency 2pq and by means of C2 the system is given an electrical resonance at frequency q. Current components of other freof frequency 2p, which will sustain mechanical vibration of the fork at that frequency. This varying condenser, as in the previous cases, is a non-linear reactance. When the generator electromotive force Ep is impressed the fork F will start vibrating at a frequency 2p and there will be transient current components at the'resonant frequencies 2p-q and q. The component 2p--q will modulate in the condenser producing a component q (the difference component between 2p and Zp-q) which will reenforce the transient component at that frequency. Simultaneous, the component of frequency q will modulate in the condenser, producing a difference frequency component Zp-q which will reenforce the transient current component at that frequency. This process of mutual reenforcement will sustain these two components of current with energy drawn from the condenser, which, of course, obtains it from the source E In the modification illustrated in Fig. 5, the electromechanical coupling is magnetic by means of iron core coil L. The input is tuned, as in the other examples of magnetic coupling, by means of a condenser C1 and inductance L1. The remainder of the system is the same as that of Fig. 4 and the operation is essentially the same.

What is claimed is:

1. A frequency changer adapted to produce sustained oscillations of a lower frequency when excited by oscillations of a single fixed frequency comprising a circuit tuned to a desired low frequency, a second circuit including a wave source of fixed higher frequency, a variable reactance device common to both of said circuits comprising an electrical reactance element and mechanical means for varying the reactance of said element responsively to variations of electrical en-- ergy therein, and means including said variable reactance device for selectively absorbing energy at a frequency corresponding to a lower side frequency resulting from the modulation of currents of said desired low frequency and currents from 3. A system in accordance with claim 1 in 75 which the said mechanical means comprises a mechanical vibrator tuned to a frequency equal to twice the wave source frequency and in which the selective energy absorbing means comprises an electric circuit including the said variable reactance device tuned to a frequency equal to the difference of the frequency of said vibrator and the desired low frequency.

4. A frequency changer adapted to produce sustained oscillations of-a lower frequency when excited by oscillations of a single fixed frequency comprising a load circuit tuned to a desired low frequency,

armature in the field of said coil, said armature being tuned to a frequency equal to the difference a second circuit including a wave source of fixed higher frequency, a coil common to both of said circuits, and a mechanically tuned of said wave source frequency and said desired low frequency.

5. A frequency changer adapted to produce sustained oscillations of a lower frequency when excited by oscillations of a single fixed frequency comprising a load circuit tuned to a desired low frequency, a second circuit including a wave source of fixed higher frequency, a coil common to both of said circuits, a mechanically tuned armature in the field of said coil having a resonance frequency of twice the wave source frequency, and a third circuit including said coil tuned to a frequency equal to the difference of the resonance frequency of said armature and the said desired low frequency.

j RALPH V. L. HARTLEY. 

